When the condition is not currently present, but is indicated in DTC history,
the cause may be intermittent. An intermittent may also be the cause when there is
a customer complaint, but the symptom cannot be duplicated. Refer to the Symptom Table
of the system that is suspect of causing the condition before trying to locate an
intermittent condition.
Most intermittent conditions are caused by faulty electrical connections or
wiring. Inspect for the following items:
| • | Wiring broken inside the insulation. |
| • | Poor connection between the male and female terminal at a connector. |
| • | Poor terminal to wire connection. Some conditions which fall under this
description are poor crimps, poor solder joints, crimping over the wire insulation
rather than the wire itself, and corrosion in the wire to terminal contact area, etc. |
| • | Pierced or damaged insulation can allow moisture to enter the wiring causing
corrosion. The conductor can corrode inside the insulation, with little visible evidence.
Look for swollen and stiff sections of wire in the suspect circuits. |
| • | Wiring which has been pinched, cut, or its insulation rubbed through may
cause an intermittent open or short as the bare area touches other wiring or parts
of the vehicle. |
| • | Wiring that comes in contact with hot or exhaust components. |
Testing for Proper Terminal Contact
It is important to test terminal contact at the component and any in‐line
connectors before replacing a suspect component. Mating terminals must be inspected
to ensure good terminal contact. A poor connection between the male and female terminal
at a connector may be the result of contamination or deformation.
Contamination may be caused by the connector halves being incorrectly connected.
A missing or damaged connector seal, damage to the connector itself, or exposing the
terminals to moisture and dirt can also cause contamination. Contamination, usually
in the underbonnet or underbody connectors, leads to terminal corrosion, causing an
open circuit or intermittently open circuit.
Deformation is caused by probing the mating side of a connector terminal without
the correct adapter. Other causes of terminal deformation are incorrectly joining
the connector halves, or repeatedly separating and joining the connector halves. Deformation,
usually to the female terminal contact tang, can result in poor terminal contact causing
an open or intermittently open circuit.
Round Wire Connectors
Follow the procedure below in order to test terminal contact:
- Separate the connector halves.
- Visually inspect the connector halves for contamination. Contamination
may result in a white or green build-up within the connector body or between terminals.
This causes high terminal resistance, intermittent contact, or an open circuit. An
underbonnet or underbody connector that shows signs of contamination should be replaced
in its entirety: terminals, seals, and connector body.
- Using an equivalent male terminal test that the retention force is significantly
different between a good terminal and a suspect terminal. Replace the female terminal
in question.
Control Module/Component Voltage and Grounds
Poor voltage or ground connections can cause widely varying symptoms.
| • | Test all control module voltage supply circuits. Many vehicles have multiple
circuits supplying voltage to a control module. Other components in the system may
have separate voltage supply circuits that may also need to be tested. Inspect connections
at the module/component connectors, fuses, and any intermediate connections between
the voltage source and the module/component. A test lamp or a Digital Multimeter may
indicate that voltage is present, but neither tests the ability of the circuit to
carry sufficient current. Make sure that the circuit can carry the current necessary
to operate the component. Refer to
Circuit Testing and
Power Distribution Schematics. |
| • | Test all control module ground and system ground circuits. The control
module may have multiple ground circuits. Other components in the system may have
separate grounds that may also need to be tested. Inspect grounds for clean and tight
connections at the grounding point. Inspect the connections at the component and in
splice packs, where applicable. Make sure that the circuit can carry the current necessary
to operate the component. Refer to
Circuit Testing and
Ground Distribution Schematics. |
Temperature Sensitivity
| • | An intermittent condition may occur when a component/connection reaches
normal operating temperature. The condition may occur only when the component/connection
is cold, or only when the component/connection is hot. |
| • | Freeze Frame, Failure Records, Snapshot, or Vehicle Data Recorder data
may help with this type of intermittent condition, where applicable. |
| • | If the intermittent is related to heat, review the data for a relationship
with the following: |
| - | High ambient temperatures. |
| - | Underbonnet/engine generated heat. |
| - | Circuit generated heat due to a poor connection, or high electrical load. |
| - | Higher than normal load conditions, towing, etc. |
| • | If the intermittent is related to cold, review the data for the following: |
| - | Low ambient temperatures. In extremely low temperatures, ice may form
in a connection or component. Inspect for water intrusion. |
| - | The condition only occurs on a cold start. |
| - | The condition goes away when the vehicle warms up. |
| • | Information from the customer may help to determine if the trouble follows
a pattern that is temperature related. |
| • | If temperature is suspected of causing an intermittent fault condition,
attempt to duplicate the condition. Refer to
Inducing Intermittent Fault Conditions, in order
to duplicate the conditions required. |
Electromagnetic Interference (EMI) and Electrical Noise
Some electrical components/circuits are sensitive to electromagnetic interference
(EMI) or other types of electrical noise. Inspect for the following conditions:
| • | An incorrectly routed harness that is too close to high voltage/high current
devices such as secondary ignition components, motors, generator etc. These components
may induce electrical noise on a circuit that could interfere with normal circuit
operation. |
| • | Electrical system interference caused by a malfunctioning relay, or a
control module driven solenoid or switch. These conditions can cause a sharp electrical
surge. Normally, the condition will occur when the malfunctioning component is operating. |
| • | Incorrect installation of non-factory or aftermarket add on accessories
such as lights, amplifiers, alarm systems, mobile phone kits, etc. These accessories
may lead to interference while in use, but do not fail when the accessories are not
in use. Refer to
Checking Aftermarket Accessories. |
| • | Test for an open diode across the A/C compressor clutch and for other
open diodes. Some relays may contain a clamping diode. |
| • | The alternator may be allowing AC generated noise into the electrical
system. |
Incorrect Control Module
| • | There are only a few situations where reprogramming a control module is
appropriate: |
| - | A new service control module is installed. |
| - | A control module from another vehicle is installed. |
| - | Revised software/calibration files have been released for this vehicle. |
| | Important: Do not re-program the control module with
the same software/calibration files that are already present in the control module.
This is not an effective repair for any type of concern.
|
| • | Verify that the control module contains the correct software/calibration. If
incorrect programming is found, reprogram the control module with the most current
software/calibration. |
